NAME

AFFILIATION

DESCRIPTION

All else being equal, complicated code is more error-prone and more expensive to maintain than simpler code. The first step towards managing complexity is to establish formal complexity metrics. One such metric is the McCabe score, which describes the number of possible paths through a block of code. This Policy approximates the McCabe score by summing the number of conditional statements and operators within a block of code. Research has shown that a McCabe score higher than 20 is a sign of high-risk, potentially untestable code. See http://en.wikipedia.org/wiki/Cyclomatic_complexity for some discussion about the McCabe number and other complexity metrics.

The usual prescription for reducing complexity is to refactor code into smaller subroutines. Mark Dominus book "Higher Order Perl" also describes callbacks, recursion, memoization, iterators, and other techniques that help create simple and extensible Perl code.

CONFIGURATION

The maximum acceptable McCabe score can be set with the max_mccabe

configuration item. If the sum of all code outside any subroutine has a McCabe score higher than this number, it will generate a Policy violation. The default is 20. An example section for a .perlcriticrc:

[Modules::ProhibitExcessMainComplexity]
max_mccabe = 30

NOTES

"Everything should be made as simple as possible, but no simpler."
-- Albert Einstein

Complexity is subjective, but formal complexity metrics are still incredibly valuable. Every problem has an inherent level of complexity, so it is not necessarily optimal to minimize the McCabe number. So don't get offended if your code triggers this Policy. Just consider if there might be a simpler way to get the job done.